The use of watercraft lifting devices is well known. A watercraft may be subject to several difficulties if moored within the water: damage to the watercraft may occur when wave action or other in-water forces cause the hull of the watercraft to strike adjacent in-water structures such as docks or seawalls; damage may also result from longer term effects such as vegetative buildup on the hull of the watercraft. Watercraft lifting devices alleviate these potential hazards by allowing the watercraft user to lift the watercraft from a position in the water to a position where the watercraft is wholly above the water. The watercraft lift thus provides a convenient solution to the before-stated difficulties since the watercraft may be quickly removed from the water during periods of non-use and returned to the water when desired with minimal user effort.
Existing watercraft lifts, however, do not sufficiently address problems caused by fluctuating water levels and/or consistently shallow waters. In water bodies where watercraft are typically used, water levels may fluctuate dramatically on a daily or seasonal basis due to tides, weather-related draught or flooding, or because of public or private use of water from reservoirs or lakes. Watercraft moorage facilities may also be situated in waters that are continually shallow. ‘Drive-on’ style lifts have very little lifting range. Lifts with translating bunks provide adequate range, but do not function in extreme shallow water. Existing translating bunk watercraft lifts may become functionally useless when water levels drop below a certain point. This occurs when the watercraft support platform, typically consisting of supporting bunks, is sufficiently high in the lowered position relative to the watercraft and waterline that friction forces between the watercraft and support platform cause watercraft ingress or egress to become impossible or unsafe.
Generally, watercraft lifts do not employ specific features that allow the lifts to operate in extreme shallow water. U.S. Pat. No. 5,908,264 to Hey and U.S. Pat. No. 518,914 to Basta disclose free-standing boat lifts with translating bunks that operate in this a manner. Since lifts are typically used along the shoreline, water depth has limited use of free-standing lifts for many locations. Certain existing watercraft lifts, however, attempt to address the above issues by using roller devices as the primary watercraft support platform. These watercraft lifts, however, are generally not as desirable due to limitations in lifting range, and that they require means to keep the boat from rolling off the bunks.
U.S. Pat. No. 6,006,687 to Hillman and Vierus employs rollers to allow a watercraft to enter and exit a channel within a modular floating system. This device, however, is limited in that the watercraft can be loaded on the lift smoothly, since the rollers need to be positioned high enough to lift the hull out of the water. The geometry lifts the front of the boat to approximately 30 degrees, which is widely considered to be undesirable to the user. Larger watercraft will require larger modular floating units that, in turn, will increase the minimum water level at which the lift will function properly. In addition, consumers on bodies of water that do not fluctuate much prefer using a freestanding lift, to eliminate effects from waves.
Two known devices use rollers to facilitate watercraft movement up a slope and out of the water. U.S. Pat. No. 5,499,247 to Smith discloses a watercraft lift with two stable rear legs and a front leg that is adjustable. Roller devices positioned on a central support beam are used to support the watercraft and to facilitate ingress and egress. The front of the boat is pulled on the lift using a winch. The watercraft needs to be stored with a front hook, to prevent the watercraft from accidental re-launching. This device is limited, since it requires a person connect the winch to the front of the boat, and winch the boat on the lift. This typically requires the user to disembark from the boat, which is undesirable. Similarly, the lifting height range of this device is limited, so the watercraft may remain subject to damage from moderate wave action or other perils meant to be avoided by the use of a watercraft lift. U.S. Pat. No. 6,520,728 to Schwitters is similar to Smith, but has the additional feature that allows the user to power on the lift without attaching the front of the boat to the winch. This invention also fails to address watercraft protection issues in that the aft portion of the watercraft is not significantly lifted from the water and may remain subject to damage from wave action as a result. Not lifting the rear of the boat from the water is undesirable, since most boat engines are in the rear. Again, relatively steep slope angles may cause additional operator difficulties when attempting to use the watercraft.
Accordingly, there is a need in the art for an apparatus that can convert existing free-standing translating bunks boat lifts for use in shallow water to get the benefit of sufficient lifting range, with the ability to be used in most locations.